Williams 2005.

Study characteristics
Methods	Randomized controlled parallel‐group trial.
Participants	60 participants with chronic non‐specific LBP. Setting: setting of trial not described. Yoga delivered in a community yoga studio. Country: USA. Recruitment: physician and self‐referral. Local physicians were informed about the study through lectures and mailed announcements. Project was announced to the public through flyers, public radio, and local university list serve for faculty and staff. Inclusion criteria: ambulatory English‐speaking men and women aged > 18 years with history of LBP and symptom duration > 3 months. Exclusion criteria: LBP attributable to nerve root compression, disk prolapse, spinal stenosis, tumor, spinal infection, alkylosing spondylosis, spondylolisthesis, kyphosis or structural scoliosis, or a widespread neurologic disorder; presurgical candidates; involved in litigation or compensation; displayed a compromised cardiopulmonary system; pregnant; BMI > 35; experiencing major depression or substance abuse; practitioners of yoga; did not agree to "forgo other forms of CAM [Complementary Alternative Medicine] during the study." Duration and follow‐up: interventions provided for 16 weeks and an additional follow‐up at 3 months after end of treatment (7 months after randomization).
Interventions	Yoga group: (n = 30) 1 × 90‐min iyengar yoga class per week for 16 weeks. Classes used supine, seated, and standing poses; forward bends, twists, and inversions; and progressed from simple to more challenging poses. Used a range of props. Yoga group also received 16 weekly newsletters, written by physiotherapy students, on back care. Home practice: encouraged to practice at home for 30 min/day, 5 days/week. Education group: (n = 30) 16 weekly newsletters, written by physiotherapy students, on back care. Common interventions: all participants could continue usual medical care for LBP. 2 weeks before beginning of 16‐week study period, both groups received 2 × 1‐hour lectures on LBP and were given instructional handouts. Co‐interventions: participants were only eligible for the study if they agreed to "forgo other forms of CAM during the study."
Outcomes	Back‐specific function (Pain Disability Index) at 16 weeks and 7 months. Back pain (VAS from Short Form‐McGill Pain Questionnaire) at 16 weeks and 7 months. Other outcomes collected: pain‐related fears to movement, beliefs associated with adjustment to chronic pain, coping strategies, perception of self‐efficacy, spinal range of motion, and changes from baseline in medications reported at baseline.
Notes	Adverse events: 1 adverse event in the yoga group, quotes: "a subject with symptomatic osteoarthritis who was diagnosed with a herniated disc during the study…" "Review of the adverse event by a medical panel summoned by the Institutional Review Board determined that it was unrelated to the performance of yoga postures." 1 older participant in the educational control group died. Measurement of expectations or treatment preferences at baseline: none. Funding; university funding. Quote: "This project was funded by the Clinical Studies request for proposals at West Virginia University."
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomization by random number generating program.
Allocation concealment (selection bias)	Unclear risk	No details of allocation process.
Blinding of participants	High risk	No blinding as comparison was an educational intervention; outcome based on self‐assessment.
Blinding of personnel/providers	High risk	No blinding.
Blinding of outcome assessors	High risk	Participants were not blinded, and outcomes were self‐reported. Quote: "Data collectors were blind to the subject's treatment status."
Incomplete outcome data (attrition bias) All outcomes	High risk	Attrition 20% in control group and 33% in yoga group at 16 weeks; 2 withdrawals linked to yoga intervention.
Selective reporting (reporting bias)	Unclear risk	Protocol not available.
Group similarity at baseline	Unclear risk	Quote: "Higher functional ability on the BPSES [Back Pain Self‐Efficacy Scale] (P=0.005), lower catastrophizing as a coping strategy (P=0.007), and less perceived disability (P=0.002) and harm (P=0.02) on the SOPA [Survey of Pain Attitudes] by the yoga group compared to the control group."
Co‐interventions	Low risk	No difference in medication use at baseline; drug use in yoga group reduced; postintervention assessment showed non‐significant differences in medical or non‐medical treatment, or lifestyle changes.
Compliance	Low risk	Quote: "Of the 20 subjects completing the yoga intervention [out of 30 randomized], an attendance rate of 91.9% was achieved for the 16‐week protocol."
ITT analysis	Unclear risk	No mention of ITT; non‐completers compared with completers.
Timing of outcome assessments	Low risk	Outcome assessment at set time points.
Other bias	Low risk	No other biases identified.